The rocker “went nuts” when a guest at a party at the Standard Hotel opened an unlocked bathroom door and saw her on the toilet with her skirt around her ankles.

According to the astonished, unintentional intruder, Love flew out of the loo, launched herself at him and threatened to have him thrown out.

Sebastian Karnaby, a pharmacist, tells Page Six he was trying to leave the party for the Times’ T style magazine at the hotel’s new Boom Boom the other night when he had the encounter with Love.

He said, “I couldn’t find my way out and asked someone to show me the door.” He opened the door he was led to, and “there was Courtney Love, sitting on the toilet with her skirt around her ankles.”

Karnaby says he was shocked and slammed the door shut, but that wasn’t enough for Love. He relates, “She stormed out screaming, ‘I am going to get you thrown out!’ She jumped on me, went crazy and dragged me over to security by the arm and claimed that I’d attacked her.

“They were trying to calm her down, but she was out of control. She was like a possessed woman.

“I absolutely did not attack her — I was trying to get away,” Karnaby said. “Thankfully, she’d remembered to pull up her skirt.”

He says security told him, “It’s best you get away as fast as possible.”

“I never wanted to see Courtney Love on the toilet,” he said. “It wasn’t a pretty sight. I just wanted to get out of there.”

Enjoying the party in a more civilized fashion were editor Stefano Tonchi, co-hosts Jeff Koons and Simon Doonan, Josh Hartnett, Helena Christensen, and photographer Terry Richardson.

Other guests at the party confirmed Karnaby’s story. Love’s rep refused to comment.